So I'm moving to new apartment soon and need some artwork to cover my walls. Is there any websites which sell game-related posters or wall art ("flags") ?

I was thinking some bands have these king of huge "flags" made of cloth which you can hang on your wall in your house so maybe there could be similar flags also for games.

By "flags" I mean posters which are at least 100x100cm in size or so.

http://store.gamesas.com/ has some artwork from a few game series, Skyrim included.

Yeah they have some Skyrim/Elder Scrolls themed items in their store but almost no posters from these brands. There are quite a few of these flags in Amazon.com but I haven't bought anything from there so I guess quality can be anything.

http://www.amazon.com/Scrolls-Skyrim-38inch-24inch-Printing/dp/B00DTTAYTQ/

http://www.amazon.com/Scrolls-Skyrim-43inch-24inch-Printing/dp/B00DTTCFD4/

These two are something I'm looking for, though they still could be larger in size.

Could always have some printed -- just look online for images that you like and have a local print shop print them for you -- DO a google search and set it to display images that are >8MP in the advanced search options - find a couple shots that you like and download them to a USB thumbdrive take them to a local copy shop ( Walmart has 16x20 prints for around $13 or 20x30 for $19 - other online sites may be cheaper) - you can upload the pics to them and they'll print and send to your local store for pick up. ) Just be sure the image is a large size jpg image (8MP +) and they should look fine when printed (if you have Photo shop you can download the image and adjust to your liking before uploading for printing)